Pressube gauge



NW4, 1941. F, BUECHMANN Re. 21,934

PRESSURE GAUGE Original-Filed Dec. 13, 1958 INVENTOR. FREDERICK B UECHMA/VN BY K 1 S A ATTORNEY.

. Reissued Nov. 4, 1941 7 1 UNITED STATE PRESSURE GAUGE Frederick Buechmann, New York, N. Y., assignor to Certiiied Gauge Instrument Corporation, a corporation of New York Original No. 2,239,691, dated April 29, 1941, Serial No. 245,478, December 13, 1938; Application for'reissue June 28, 1941, Serial No. 400,331

7 Claims.

This invention relates to new and useful improvements in indicating devices and relates more particularly to an improved movement for measuring and indicating instruments generally,

and more specifically devices for indicating fluid pressure.

The so-called Bourdon type oipressure gauge has been in rather extensive use for many years, such gauge comprising a bronze tube of elliptical cross-section, said tube being bent into .a substantially circular form. One end of this tube is soldered to a central block positioned within a casing, the fluid entering such block and passing into the tube. The opposite end of the tube is sealed and in the usual run '01 prior art devices, this .end is connected by means 01 a link to a pivoted, curved rack portion, the teeth oiwhich' mesh with those of a pinion on a pointer shalt. In order to prevent the backlash or other free play between the teeth of the rack and pinion, a hair spring is usually employed for the purpose oi exerting constant pressure on the pinion. This type of movement is, howeverprelatively unsatisfactory for the reason that despite the presence of the spring, backlash is not eliminated and, as the result, the readings taken are frequently inaccurate. Another reason for the inaccuracy in a movement oi this character which converts the movement 01' the end of the tube into rotary movement, is in the fact that it is impossible to make the teeth sufficiently accurate within the cost limits of a reasonably priced article to provide an accurate gauge.

The present invention is directedprimarily to an improved type of mechanical movement for I use in this connection, the movement including a pivoted sector cam structure, preferably made irom sheet metal. This pivoted cam has a link connection with the free end oi the tube and is the driving element of the movement. A cylindrical cam structure, the driven element, is

impossible to avoid a very considerable amount oi free play between the rack and pinion, since it a tight engagement were-provided, the parts would not freelymove. In the present invention, however, the sector cam may be made of material of substantiallythe same thickness as the width of the spiral cam slot in the cylindrical cam structure. Thus 'a relatively tight flt is provided between the base-walls oi the cam slot, without, however, causing any; binding or lack 0! free motion. Thus, as the pressure within the tube increases and causes the free end thereof to make its substantially longitudinal movement, the sector cam moves through an arc by virtue of-its link connection with the free end 0! the tube, thus causing the cylindrical cam structure to rotate in strict accordance with the movement of the free end of the tube.

From the foregoing it will be obvious that one of the principal objects of the invention is the provision of an indicating instrument having a movement oi fargreater accuracy than was posmounted upon and keyed to the pointer shai't,

such cam structure being formed with a spirally disposed annular recess having a predetermined angle relative to the plane of rotation 01 the pointer shaft. The sector cam is appropriately formed to have its cam face on the same angle relative to its plane of. rotation as is the spiral recess, the opposed cam surfaces of such sector cam engaging the side walls of the annular spirally disposed recesses in the cylindrical cam structure.

In the prior art devices 0! the type previously described and employing the quadrantal pivoted rack. and the pinion on the pointer shalt, it was sible by the useoi' the old type of movement,

Another object of the invention is the provision of an improved movement for pressure gauges wherein the amount of wear is greatly minimized and the gauge will enjoy a far longer life than is possible with the old type oi structure.

A further object 01' the invention is the provision of a relatively inexpensive pressure gauge wherein the possibility of backlash is eliminated.

Yet another object of the invention is to provide an improved indicating instrument with novel means for eflecting an adiustment of the parts.

In the drawing:

Fig. 1 is a front elevation of the preferred embodiment oi the present invention, the view showing the casing for the pressure gauge in broken lines;

F 8. 2 is a 0! P18. 1;

. modified form 01' sector cam:

Fig. 4 is. a front elevation of the cylindrical cam with its annular spirally disposed cam surface,

the view also showing the modified form of secvertical section taken on line 2-2 through which the fluid enters, such block having a threaded portion II to enable it to be secured to the fluid conduit. This,block is mounted in a suitable aperture II at the lower end of a circular casing It by means of screws It. The pressure tube I6 is preferably made from bronze unless it is to be used in extremely high pressures, in which case steel is the more preferred material. This tube is, as shown in Fig. 2, elliptical in transverse section and is bent into a substantially circular form, one end of the tube being suitably secured at l"| to the block, the usual fluid connection being provided between the block and the tube. The sector cam I9 is portion is provided with an extension portion H,

the end of which is provided with a transverse extension 43, This portion 43, as well as a pertion of the extension 42, is bent at right angles Accordingly, when it is desired to make some adjustment between the sector cam and the closed end of the tube, this U-shaped portion is readily preferably made from flat sheet metal and is provided with a bearing portion 2|! for mounting the same upon a pivot II, which pivot is supported between two spaced upstanding projections 22 and II of the'central block. It will be noted from an examination of Fig. 2 that the cam surface "of the sector cam is bent to form an angle relative to the plane of rotation of' the cam. The angle may vary, depending upon the nature of the particular instrument, although in actual practice, an angle of 18 or thereabouts is most satisfactory. This cam portion should be of uniform thickness throughout its length and likewise should be perfectLv fiat.

s A pointer shaft 21 is pivotally mounted between the upstand P rtions 22 and 23 adjacent to the upper ends thereof, such shaft having a pointer 2! at the front end thereof. The casing is further provided with a removable cover 28 supporting a glass face ill through which the indicator and the face of the instrument 3| may be observed, such face II having the usual graduations thereon (not shown). A1-' so mounted upon and keyed to this pointer shaft is a cylindrical, driven cam structure 33 provided with an annular spirally disposed recess .34, forming opposed cam faces. When the axes of said driven 'cam structure 33 and of cam surface II are parallel, as illustrated, the angle of the opposed cam faces relative to a ,plane of rotation of the cam structure 33 must, of course, be the same as the angleof the cam face 25 relative to a plane of its rotation. In other words, said cam face 25 must lie in a plane corresponding to the lead angle of the spiral recess, 1. e., the angle between the cam face of the spiral recess and a plane of its rotation, thus causing the sector cam to exert a thrust against the spiral cam face imparting rotative motion thereto and causing progressive engagement between the respective cam uniform throughout its length, is desirably substantially the ,same as the thickness of the material from which the sector cam is constructed. The fit should not be so tight as? to cause any binding, although it must be sufllciently close in order to provide substantially no lateral movement of the sector cam within the recess.

The sector cam is further provided with a curved extension portion It to which is secured a link 31. Between this link 31 and the free end of the tube, a substantially U-shaped adjustment link II is positioned. This link is shown in detail in Fig. 5 and comprises a terminal portion I! having an aperture ll thereinto provide connection between this link-and the link TI. The ormosite terminal ll of this U-shaped faces. Also, the width of the slot, which must be bent to bring the spaced arms of this U-shaped portion toward or away from each other,. as the case may be. 1

The modification of the invention illustratedin Figs. 3 and 4 comprises a sector cam 46 having a bearing portion 41, this cam, however, being made from relatively thinner material than the cam in the first embodiment, the cam further having an adapter spring 48 of exactly the same size and contour as the cam itself. The adapter spring 48 is so adjusted relative to the cam as to cause the opposed faces of cam and spring to lightly engage the opposed faces of the recesses 34 in the cylindrical cam, thereby providing an accurate transmission of movement from the tube to the pointer shaft.

- It will be appreciated that whereas the foregoing movement is shown in connection with a fluid pressure gauge of the sorcalled Bourdon type, it will nevertheless have many other uses in measuring instruments of all descriptions.

The foregoing structures may be considerably modified without departing from the spirit of the invention. For instance, instead of employ-- ing the pivoted cam, a substantially centrally pivoted lever or bell crank lever may be employed, one end of such lever being actuated by the measuring device and the other end driving the cylindrical cam.

What I claim is:

1. In a pressure gauge having a pointer shaft, a pointer carried thereby and a curved pressure tube elliptically shaped in transverse section, one

end of such tube being fixed and operatively connected with a fluid conduit, the opposite end thereof being free and closed, the combination of means connecting such free end with the pointer shaft, whereby the substantially longitudinal movement of the free end of the tube will be transmitted to the shaft, such means comprising a pivoted sector driving cam plate, a link connecting the free end of the tube with such. cam plate, the cam surface of such plate lying on one plane and at an angle to a plane of rotation of the cam plate, and a cylindrical sleeve mounted vsleeve mounted on-the pointer shaft and having a spiral recess therein having a substantially uniform lead angle throughout its length, a pivotally mounted sector cam plate operativelyconnected with the free end of'the pressure tube and having a cam surface lying on a plane corresponding to the lead angle of the spiral recess, such cam surface residing in said recess and adapted to *same size as the cam plate adapted to y el impart mauve movement to the pointer shaft.-

3. A fluid pressure indicator comprising a preslnre tube, a pointer shaft and a pointer carried thereby and means for transmitting movement from the free end of the pressure tube to the pointer shaft, such means including a cylindrical sleeve associated with the pointer shaft having a spiral groove of substantially uniform width and lead angle throughout its length, a pivotally mounted sector cam structure formed in two complemental portions of substantially the same size and shape, the cam portions of the cam structure being positioned within said recess and adapted to yieldingly engage the opposed edges thereof, such cam portions lying on a-plane corresponding to the leadvangle of the spiral recess and adapted to impart rotative movement to the sleeve as the cam plate turns under the actuation of the pressure tube.

a spiral groove having a substantially uniform lead angle throughout its length, a pivotally mounted sector cam plate operatively connected with the free end of the pressure tube and adapted to drive the sleeve, the cam portions of such cam plate lying on a plane corresponding to the lead angle of the spiral recess, one surface of such cam plate engaging one edgeof the recess, and a spring pressed adapter'plate of substantial] the y engage the other edge of the recess. 1

5. A fluid pressure gauge including a frame,.'a pressure tube rigidly mounted at one end theietf on the frame and being free to; move at its opposite end, a plurality of shaf iournalled in the frame, a pointer carried one of the shafts and means for providing an operative connection between the free end of the pressure tube and the pointer shaft to translate the substantially reciprocating movement of'the free end of the tube to rotative movement of the pointer shaft, saidmeans comprising a driving cam and a driven cam mounted on the several shafts and means connecting the driving cam with the free end of the tube, one of such cams being generally cylincal in shape and having an annular spiral recess therein having a substantially uniform lead angle throughout its length, the other cam being formed with a cam surface lying on a, plane corresponding to the lead angle of the spiral recess and being positioned within said recess.

,6. A fluid pressure gauge including a frame, a pressure tube rigidly mounted at one end thereof on theframe and being 'free to move at its opposite end, a plurality of shafts journalled in the frame, a pointer carried on one of the shafts and means for providing an operative connection between the free end of the pressure tube and the pointer shaft totranslate the substantially reciprocating movement of the free end of the tube to rotative movement of the pointer shaft, said means comprising a driven cam mounted on the pointer shaft and a driving cam on a second shaft, and means connecting the driving cam with the free end of thetube comprising a substantially U-shaped link, the driven cam being generally cylindrical in shape and having an annular spiral recess therein having a substantially uniform lead angle throughout its length, the driving cam being formed with a cam surface lying on a plane corresponding to the lead angle of the spiral recess and being positioned within said recess.

7. In a measuring instrument having means responsive to changes in conditions and being formed with an element which is movable in accordance with such changes in conditions, the combination '01 a pointer shaft, a pointer carried thereby, and means for transmitting the movement of the responsive element to the pointer shaft, said means comprising a driven, spiral cam provided on the indicator shaft, 9. driving, sector cam plate pivotally mounted on an axis substantially parallel to the pointer shaft, operatively connected with said responsive element andllying at an. angle corresponding generally to the lead angle of the driven spiral cam, the cam plate exerting a vthrust against the face of the spiral cam imparting rotative motion thereto and causing progressive engagement between the respective faces of the sector cam plate and the spiral cam.

= BUEC M N- 

